block: ensure we hold a queue reference when using queue limits

q_usage_counter is the only thing preventing us from the limits changing
under us in __bio_split_to_limits, but blk_mq_submit_bio doesn't hold
it while calling into it.

Move the splitting inside the region where we know we've got a queue
reference. Ideally this could still remain a shared section of code, but
let's keep the fix simple and defer any refactoring here to later.

Reported-by: Christoph Hellwig <hch@lst.de>
Fixes: 900e08075202 ("block: move queue enter logic into blk_mq_submit_bio()")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f57b86d6de6acf9bf2df260ba0cc4aad59156926..e02c4b1af8c552c8b8cb4dfb8b3ce4edf1eacf2c 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2964,12 +2964,6 @@ void blk_mq_submit_bio(struct bio *bio)
        blk_status_t ret;
 
        bio = blk_queue_bounce(bio, q);
-       if (bio_may_exceed_limits(bio, &q->limits)) {
-               bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
-               if (!bio)
-                       return;
-       }
-
        bio_set_ioprio(bio);
 
        if (plug) {
@@ -2978,6 +2972,11 @@ void blk_mq_submit_bio(struct bio *bio)
                        rq = NULL;
        }
        if (rq) {
+               if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {
+                       bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
+                       if (!bio)
+                               return;
+               }
                if (!bio_integrity_prep(bio))
                        return;
                if (blk_mq_attempt_bio_merge(q, bio, nr_segs))
@@ -2988,6 +2987,11 @@ void blk_mq_submit_bio(struct bio *bio)
        } else {
                if (unlikely(bio_queue_enter(bio)))
                        return;
+               if (unlikely(bio_may_exceed_limits(bio, &q->limits))) {
+                       bio = __bio_split_to_limits(bio, &q->limits, &nr_segs);
+                       if (!bio)
+                               goto fail;
+               }
                if (!bio_integrity_prep(bio))
                        goto fail;
        }